David Travis talks through 7 points around prototyping myths. Not sure that I agree with each one 100%, but all the points are good prompts to think more about how and why we prototype. Plus there are some great links to resources and further reading.
David's article talks in the main about the prototype itself. Personally, I'm not particularly concerned about how it was made or the semantics of what a mockup, wireframe or prototype is.
For me, it's about what you do with it. Prototyping the verb is what it's all about. Not prototype, the noun.
Also, the article views each creation method as unique and independent. I find my prototyping tends to draw on multiple techniques. Visio to create a framework plus some (or pretty much all) of the design idea, then layers of scribbles on a print out. Sometimes with a doctored screenshot integrated too.
Make sure you scroll to the end of the article. There's a great video of someone replicating interaction with their paper prototype.
7 myths about paper prototyping - article by David Travis for userfocus.co.uk